Compactors are machines used to compact initially loose materials, such as asphalt, soil, gravel, and the like, to a densified and more rigid mass or surface. For example, during construction of roadways, highways, parking lots and the like, loose asphalt is deposited and spread over the surface to be paved. One or more compactors, which may be self propelling machines, travel over the surface whereby the weight of the compactor compresses the asphalt to a solidified mass. The rigid, compacted asphalt has the strength to accommodate significant vehicular traffic and, in addition, provides a smooth, contoured surface that may facilitate traffic flow and direct rain and other precipitation from the road surface. Compactors are also utilized to compact soil or recently laid concrete at construction sites and on landscaping projects to produce a densified, rigid foundation on which other structures may be built.
Various types of compactors are known in the art. For example, some compactors include a rotatable roller drum that may be rolled over the surface to compress the material underneath. In addition to utilizing the weight of the roller drum to provide the compressive forces that compact the material, some compactors are configured to also induce a vibratory force to the surface. As can be appreciated, the vibratory forces assist in working or compacting the loose materials into a dense, uniformly rigid mass. To generate the vibratory forces, one or more weights or masses may be disposed inside the roller drum at a position off-center from the axis line around which the roller drum rotates. As the roller drum rotates, the off-center or eccentric position of the masses induce oscillatory or vibrational forces to the drum that are imparted to the surface being compacted. In some applications, the eccentrically positioned masses are arranged to rotate inside the roller drum independently of the rotation of the drum.
For example, U.S. Pat. No. 7,213,479 describes a vibratory mechanism in which two vibratory shafts are stored in a roll. The vibratory shafts include one or more eccentric weights disposed thereon and are configured to rotate inside the roll so that the eccentric weights generate an oscillating or vibratory force. Inside the roll, the vibratory shafts are parallel to each other and the rotational axis of the roll with the first and second vibratory shafts arranged 180° opposite each other with respect to the rotational axis of the roll. Further, the vibratory shafts cooperate with each other to vibrate the roll in various radial and tangential directions depending on the direction that the shafts are rotated.
As can be appreciated, it may be possible to vibrate or oscillate the roller drum in predetermined and particularized directions that improve the rate and degree of compaction of the material, that is, to focus the vibratory forces onto the surface being compacted. An opposing concern is to minimize or isolate the vibrations of the roller drum to avoid determinately effecting the operation of the compactor.